don't think it is possible
after doing more research myself into the API and such, i don't believe that microsoft gives you a method to do it. if you do widen the scrollbars, i have found that the height of them does not change significantly. the only way i could figure out to do it would be to trick the area surrounding the listbox into thinking it was a lower resolution. not practical. so anyway, i am off to write an activex control of my own to do a larger version of the listbox and maybe the combobox.
good luck